Q3 – Can the correct cable cleat be specified based only upon the cross sectional area of the cable conductors?

A3 – No, the cable cleat retains around the outside diameter of the cable – see A2.

Q4 – I am confused but impressed by the level of customer choice with respect to triplex cable cleats. Why are there so many Ellis cleat options?

A4 – It is important that when selecting cable cleats for high voltage triplex cables that the cable cleats can handle the anticipated fault currents especially at working voltages of 11kV/33kV – also, different DNO’s specify different cleats.

Q5 – In order to retain high voltage power cables we require cable cleats with high fault rating but are concerned about potential outer cable sheath damage to “soft-sheathed” type power cables with EPR insulation. Typical oil rig application.

A8 – Stainless steel and aluminium cable cleats are both non-magnetic and unaffected by magnetic fields surrounding low and high voltage power cables. Cables fixed with cable cleats made from magnetic materials would cause localised heating of cleated cables by the effects of induction.

Q9– What is galvanic corrosion and how may it impact on cable cleat installations?

A10 – Of course, here goes. As manufacturers of cable cleats, Ellis Patents are frequently asked for advice on the correct method of securing multi-core power cables.

We are not aware of any published data, which indicates any particular fixing method but custom and practice suggests that most users presume that any forces on the conductors, which arise in the event of a short circuit, will be restrained within the cable jacket and therefore cable cleats are not required.

The mechanisms within a multi-core cable, which help restrain the conductors in the event of a short circuit include:

1.The outer extruded jacket

2. The helical winding of the cores

3. Steel wire or other type of armour if present

In order to be able to provide meaningful advice Ellis Patents undertook a series of short circuit tests using 3 core, copper conductor, multi-core cables from various cable manufacturers.

Both armoured and unarmoured cables were tested across a variety of conductor sizes but because of the number of manufacturers and the variety of cable types and methods of construction available, it was not feasible to carry out exhaustive tests.

The results of the tests were varied but clearly showed that it is unsafe to presume that the forces between the conductors will always be restrained within the jacket of the cable, whether or not the cable is armoured or tightly helically wound.

If you are planning a project and would like certainty regarding the cable fixings for your installation (whether single or multi-core cables are included in the design) T&D and Ellis Patents would be interested to conduct a bespoke test, on your behalf, within our regular programme of work.